We had this one a long time ago, and Estelle found the answer, but I can't locate the thread using a search. It must have aged out. Let's see what I can remember.

The individual for whom the step is named was a contemporary of Louis XIV, and was the Comte de Sissonne, back in the day when ballet de cour was just the thing, and nobles were the dancers. Apparently this Comte de Sissonne could do these jumps from two feet to one very well and the name stuck to them. Estelle, do you have your references handy for correction or more detail?